Both indirect and direct methods are currently used for producing ear pieces for noise and swim protection, Since the demands on user comfort are very high, the dimensional accuracy and precision fit of the silicone ear piece are extremely important, Addition-crosslinking silicones have proven to be particularly suitable, which in contrast to condensation-crosslinking silicones, undergo only slight shrinkage and therefore have particularly high dimensional stability, However, condensation-crosslinking silicones may also be used.
Condensation-crosslinking silicones according to the prior art comprise (some or all of) the following components as the base mass:
(1) Polyorganosiloxanes containing two end-position hydroxyl groups in the molecule;
(2) Polyorganosiloxanes containing no reactive groups;
(3) Reinforcing fillers having a charged or uncharged surface;
(4) Non-reinforcing fillers;
(5) Oils and/or other softeners;
(6) Other additives and customary addition agents, adjuvants, and dyes;
(7) Catalytically active additives;
(8) Inhibitors;
The compounds listed under (1) are polyorganosiloxanes containing end-position reactive hydroxyl groups having a viscosity of approximately 200 mPa·s to 400,000 mPa·s, preferably 1000 mPa·s to 350,000 mPa·s, at 23° C.
The compounds listed under (2) include silicone oils, which like the compounds under (1) are polyorganosiloxanes, but which contain groups that are unreactive for the condensation crosslinking reaction. Such compounds are described, for example, in W, Noll, “Chemie und Technologie der Silikone” [Chemistry and Technology of Silicones], Verlag Chemie Weinheim, 1968.
Reinforcing fillers under (3) generally have a BET surface of greater than 50 m2/g and include, for example, pyrogenic or precipitated silicic acids and silicon-aluminum mixed oxides. In view of their hydrophilic surface, these fillers are particularly suited for use with hydroxyl polyorganosiloxanes, but may also be made hydrophobic by surface treatment with, for example, hexamethyldisilazane or organosiloxanes or organosilanes.
The non-reinforcing fillers under (4) have a BET surface of less than or equal to 50 m2/g and include quartzes, cristobalites, diatomaceous earths, kieselguhrs, calcium carbonates, talc, zeolites, sodium aluminum silicates, metal oxide powders, and glass powders. These fillers, as in the case for the reinforcing fillers, may also be made hydrophobic by surface treatment.
Examples of compounds under (5) are hydrocarbons, particularly preferably paraffin oils.
Paint pigments and other adjuvants may also be contained as additives. For controlling the reactivity it may be necessary to use catalytically active additives (7), generally water or organic acids such as benzoic acid, or inhibitors (8) such as very short-chain, end-blocked hydroxyl siloxanes.
The condensation reaction is initiated by mixing the base mass with a curing paste as a second component, The proportion of curing paste in the mixture varies from 1 to 10 percent by weight, preferably 2 to 5 percent by weight, relative to the base mass.
A curing paste according to the prior art comprises the following components:
(1) catalyst for the condensation crosslinking, generally an organotin compound such as dibutyl tin dilaurate or dibutyl tin oxide;
(2) hydrolyzable reactants, generally silicic acid esters such as vinyl triethoxysilane or tetraethyl silicate;
(3) a carrier material, generally mineral oil products such as Vaseline; and
(4) other additives and customary addition agents, adjuvants, and dyes.
The base mass may also be mixed with a curing liquid. The curing liquid is composed of only components (1) and (2) and optionally (4), i.e., is prepared without a carrier material and therefore has a low viscosity.
Addition-crosslinking silicones according to the prior art comprise (some or all of) the following components:
(1) polyorganosiloxanes containing at least two unsaturated groups in the molecule;
(2) polyorganohydrogensiloxanes containing at least two SiH groups in the molecule;
(3) polyorganosiloxanes containing no reactive groups;
(4) noble metal catalyst;
(5) reinforcing fillers having a charged or uncharged surface;
(6) non-reinforcing fillers;
(7) Oils or other softeners;
(8) Other additives and customary addition agents, adjuvants, and dyes; and
(9) inhibitors.
The compounds listed under (1) are polyorganosiloxanes containing end-position and/or side-position reactive groups having a viscosity of approximately 50 mPa·s to 165,000 mPa·s, preferably 200 mPa·s to 65,000 mPa·s, at 23° C.
The compounds listed under (2) include SiH groups which form the polymer in an addition reaction with compounds (1) under noble metal catalysis.
The compounds listed under (3) include silicone oils, which like the compounds under (1) are polyorganosiloxanes, but which contain groups that are unreactive for the noble metal-catalyzed addition crosslinking reaction. Such compounds are described, for example, in W, Noll, “Chemie und Technologie der Silikone,” Verlag Chemie Weinheim, 1968.
The noble metal catalyst (4) preferably is a platinum complex, Platinum-siloxane complexes as described in U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,775,352, and U.S. Pat. No. 3,814,730 which are particularly well suited.
Reinforcing fillers under (5) generally have a BET surface of greater than 50 m2/g and include, for example, pyrogenic or precipitated silicic acids and silicon-aluminum mixed oxides. The referenced fillers may be made hydrophobic, for example, by surface treatment with hexamethyldisilazane or organosiloxanes or organosilanes non-reinforcing fillers under (6) have a BET surface of less than or equal to 50 m2/g and include quartzes, cristobalites, diatomaceous earths, kieselguhrs, calcium carbonates, talc, zeolites, sodium aluminum silicates, metal oxide powders, and glass powders. These fillers, similarly as for the reinforcing fillers, may also be made hydrophobic by surface treatment.
Examples of compounds under (7) are hydrocarbons, particularly preferably paraffin oils.
Paint pigments and other adjuvants may also be contained as additives, for example finely divided platinum or palladium as hydrogen absorbers. It may be necessary to add inhibitors (9) to control the reactivity. Such inhibitors are known, and, for example, are described in U.S. Pat. No. 3,933,880. These inhibitors generally are acetylenically unsaturated alcohols or vinyl group-containing poly-, oligo-, and disiloxanes.
The masses are preferably formulated in two components to ensure stability under storage, The entire content of noble metal catalyst (4) should be provided in the catalyst component, and the entire content of SiH compound (2) should be provided in the second component, spatially separated from the first component, of the base mass. Mixing the two components causes the masses to cure in an addition reaction known as hydrosilylation.
The volume ratios of the two components may be from 10:1 to 1:10, Particularly preferred are volume mixing ratios of 1:1, 4:1, and 5:1 (base to catalyst component), For the paint, volume mixing ratios of 40:1 to 1:40 (base to catalyst component) are preferred.
According to the prior art, silicone ear pieces are sometimes provided with a painted surface finish, using a paint. Such a paint has the following composition:
(1) Polyorganosiloxanes containing at least two unsaturated groups in the molecule;
(2) Polyorganohydrogensiloxanes containing at least two SiH groups in the molecule;
(3) Polyorganosiloxanes containing no reactive groups;
(4) Noble metal catalyst;
(5) Reinforcing fillers having a charged or uncharged surface;
(6) Inhibitors;
(7) Organic solvent;
The previous description also applies for the ingredients (1) through (6), This paint is also a two-component material, and the above comments apply here as well. The organic solvents used according to the invention have a boiling point in the range of 40° to 200° C., preferably 70° to 150° C., particularly preferably 100° to 140° C., at 1013 hPa, Cyclic and aliphatic hydrocarbons such as cyclohexane, n-hexane, n-heptane, toluene, and benzene may be considered. The silicone ear pieces are dipped in the paint, and the paint is cured in an oven at temperatures of 140° to 200° C., Following this treatment the ear piece has a smooth, glossy surface.
Silicone ear pieces for noise or swim protection are generally worn in the ear for long periods, For this reason hygiene is particularly important. The use of silicones in the field of noise and swim protection ear pieces is known, since silicones offer a broad spectrum of mechanical and physical properties, as well as the further advantage of having little or no toxic, sensitivity, or allergenic potential. This makes them very well suited for medical applications. The precision fit of ear pieces plays a special role. The ear piece is in direct contact with the skin of the ear. The moist, warm environment in the auditory canal provides the ideal conditions for growth of microorganisms (bacteria, virus, molds, algae), and it is known that these may settle on silicones. This impairs not only the hygiene but also the esthetics of ear pieces, which are worn in the ear for long periods by persons for the purpose of noise protection, for example for occupational use, or as swim protection during swimming. Inflammations in particular may occur when the skin of the auditory canal is irritated as the result of pressure points (due to improper fit of the ear piece), or friction during chewing motions.
Imparting antimicrobial activity to the silicone materials without adversely affecting the polymerization reaction described in detail above is therefore desirable.
The protection of objects and surfaces from microorganisms has been known for many years, For example, the antimicrobial effect of silver or copper surfaces has been known for centuries although the exact mechanism was not understood. In the field of hearing aid acoustics, the firm Audio Service markets a commercial solution for coating ear pieces, based on the bactericidal and fungicidal activity of silver, under the trade mark ComforMed™.
The introduction of antimicrobial additives is also known from the field of dental impression materials. The incorporation of quaternary ammonium salts, dissolved in water, into alginates is described in EP 0 361 301. WO 00/07546 describes a silicone material used for dental impression materials which acquires antimicrobial activity by incorporation of N-chloramines and similar compounds.
The use of biguanides in addition-crosslinking silicones is known from EP-A-0 493 186.
The use of calcium hypochlorite in condensation-crosslinking silicones is documented, for example, in FR 2 707 660. In this case the effect is derived from active chlorine.
However, none of the referenced and published additives having an antimicrobial effect meet the high demands placed on polymerizable materials such as ear pieces, for example, which are worn in the ear for long periods for noise or swim protection:                The antimicrobial additive must not be toxic, and must have no sensitivity or allergenic potential.        The antimicrobial additive must be present in the polymerizable mass in sufficient quantities so that it may act on the contact surface.        The antimicrobial additive must neither inhibit the polymerization reaction nor affect the typical characteristics of the polymer.        